This invention relates to processes for preparing 2-(6-methoxy-2-naphthyl)propionic acid which is an available pharmaceutical having antiphlogistic, analgesic and antipyretic actions, for preparing 2-hydroxy-2-(6-methoxy-2-naphthyl)propionic acid which is extremely useful as a precursor for preparing the above compound, and for preparing 2-hydroxy-2-(4-substituted phenyl)propionic acid which is extremely useful as a precursor for preparing 2-(4-substituted phenyl)propionic acid which is usable as a pharmaceutical having antiphlogistic, analgesic and antipyretic actions.
As the method for preparing 2-(6-methoxy-2-naphthyl)propionic acid, there has hitherto been known the methods as disclosed in Japanese Patent Publications No. 702/1973 and No. 31981/1974.
In Japanese Patent Publication No. 702/1973, there is disclosed the method in which 2-(6-methoxy-2-naphthyl)propionic acid is prepared from 2-methoxynaphthalene via 7 steps by using sodium hydride and methyl iodide.
Also, in Japanese Patent Publication No. 31981/1974, there is disclosed the method in which 2-(6-methoxy-2-naphthyl)propionic acid is prepared from 2-naphthol via 7 steps by using dimethyloxosulfoniummethylide.
These methods are many in preparation steps and require complicated operations, and yet these methods require a substarting material which is highly dangerous or expensive so that they include many problems.
Also, as the method for preparing 2-(6-methoxy-2-naphthyl)propionic acid from 2-hydroxy-2-(6-methoxy-2-naphthyl)propionic acid or ester derivatives thereof, there are methods as disclosed in Japanese Provisional Patent Publications No. 4136/1976, No. 105144/1977 and No. 16437/1980. In the methods of these publications, they involve the problem that an expensive material such as hydroiodic acid is required. In Japanese Provisional Patent Publication No. 4136/1976, there is disclosed the method in which 2-(6-methoxy-2-naphthyl)acrylic acid is synthesized from 2-hydroxy-2-(6-methoxy-2-naphthyl)propionic acid by the dehydration reaction and then reducing the compound or the method in which 2-halogeno-2-(6-methoxy-2-naphthyl)propionic acid is synthesized from 2-hydroxy-2-(6-methoxy-2-naphthyl)propionic acid and then reducing the compound, but these methods have the problem that steps become likely longer. Also, the method disclosed in Japanese Provisional Patent Publication No. 16437/1977 requires to use expensive quaternary ammonium salts or bromoform so that it involves the problem.
Also, the conventional catalytic reduction using no acid catalyst requires a long reaction time and the reduction using a metal requires a large amount of metal. Other methods are also unsuitable methods from the industrial view point.
As the other literature of the preparative method of 2-(6-methoxy-2-naphthyl)propionic acid, there may be mentioned EP-A-0 184 573, EP-A-0 189 120 and DE-A-26 13 817 (German Offenlegungusschrift).
In the methods disclosed in EP-A-0 184 573 and DE-A-26 13 817, many producing steps and complicated operations are necessary for obtaining 2-hydroxy-2-(6-methoxy-2-naphthyl)propionic acid. In the method disclosed in EP-A-0 189 120, electrolytic reaction should be carried out so that there involves many problems.
While there is no literature describing a 2-hydroxy-2-(4-substituted)propionic acid derivatives which are one of the compounds to be prepared by the method of the present invention, if the methods disclosed in the above literatures are applied thereto, there involve the same problems as mentioned above and thus, establishment of an excellent industrial preparative method has been desired.